This invention relates to a vibration isolation system.
Specifically, the invention is directed to a pneumatic vibration isolation device of the "air spring" type which attenuates the horizontal components of disturbing vibrations, while improving the vertical isolation properties of the pneumatic device.
All buildings vibrate and vibrations transmitted through the floor affect instruments and apparatus to varying degrees. A vibration isolation system must have a natural frequency (resonate) materially below the lowest floor frequency. High frequency (over 25 Hz) vibrations can easily be attenuated with traditional static control systems such as a marble slab supported on rubber pads, cork, fiberglass, or inflated bags. Serious problems usually occur when floors vibrate at low frequencies (7-25 Hz). Most static systems resonate in or above this frequency range and therefore, actually amplify low frequency vibrations. Traditional static systems designed for low frequency vibration problems are usually too massive or too unstable to be practical for most applications. Any static low frequency system is very sensitive to load variations which cause level changes in the top surface and obvious operator problems.
Air isolation systems are not static. Typically, they have an ultra-low natural frequency which provides a high degree of both attenuation and damping. Some systems, such as the MICRO-g System, as sold by Technical Manufacturing Corporation of Woburn, Mass., have automatic self-leveling that provides high stability and zero static deflection. Typically, these air isolation systems are available as self-contained tables, bench top units, etc. They are of the "air spring" type wherein the load carrying piston is pneumatically supported and secured with a flexing element. The systems are primarily used in laboratories for such instruments as microscopes, electronic balances, etc. and in industry, such as in the manufacture of micro-miniature circuits and related components.
The prior art most pertinent to the present invention makes use of two different types of flexing elements. Both are usually a fabric-reinforced rubber flexing element. The two differ largely in height, and can be made to effect differences in the available flexure in the horizontal direction.
The first application of the flexing device is commonly described as a diaphragm device. It is flexible in the vertical direction and less so horizontally. A flexible diaphragm sealing element is allowed to roll up and down between the walls of an outer restraining ring and the side of a load bearing piston. Versions of this diaphragm device are employed with varying height and width of the annular roll portion so as to effect varying desired amounts of horizontal flexure.
A device of this type does not have nearly as effective horizontal flexure as vertical flexure. The diaphragm system has the virtues of compactness in the vertical sense and security against unwanted sway in the horizontal sense. In the typical application of the art, such a diaphragm is thin (0.010-0.025 inch) and therefore, rather easily flexed.
In the second application of the flexing element, the device is made higher, may have multiplicity of convolutions and is employed so as to make use of the extended height or convolutions to permit horizontal flexure.
Because this latter flexing element must bear a vastly greater net stress, it is typically made more robustly than the diaphragm element. It has the virtue of allowing horizontal flexure within the structure of the element itself. However, the element may be subject to excessive sway unless constrained. Sway conditions may be compounded as the element is inflated further, or if it travels to its upper range.